@Rx Enthusiast – There turned out be only one implementation of the interface, basically with "smart fields" aka properties and it was hard to imagine other types that'd implement it. So we swapped it out by a concrete EventPattern<TEventArgs> type instead.

I've been upgrading from build 1.0.2856 to 1.1.10621 and managed towork out most of the changes, but I can't work out what happened to the concurrent collections that were in System.Collections.Concurrent in the Silverlight 4 (and probably .Net35) version?